Multiple plate work coil with offset edges for induction heating



July 10, 1956 w ALBRECHT 2,754,397

MULTIPLE FL ATE WORK COIL WITH OFFSET EDGES FOR INDUCTION HEATING FiledMay 22, 1953 gww m 73 5 66 70 2 United States Patent O i MULTIPLE PLATEWORK COIL OFFSET EDGES FOR INDUCTION HEATING William B. Albrecht,Wauwatosa, Wis., assignor to Allis- Chalmers Manufacturing Company,Milwaukee, Wis.

Application May 22, 1953, Serial No. 356,667

Claims. (Cl. 21910.79)

This invention relates in general to work coils for high frequencyinduction heating of a workpiece and more particularly to an improvedwork coil of the type having each turn of the work coil formed from aflat plate.

The term workpiece as commonly used in the induction heating art and asused here refers to an object which is heated by eddy currents whichflow in the object, the eddy currents being produced through inductionby a high frequency current. The inductor which carries the highfrequency current is termed the work coil.

The utilizing of fiat plates to form conductor turns of a work coil iswell known and has proved successful in the heat treating of variouskinds of objects. This type of work coil is advantageous because it issimple to manufacture, mechanically strong and dissipates heat rapidly.

In the construction of this type of work coil each turn is usually madefrom a separate fiat plate with each plate provided with an aperture ora group of apertures for receiving the workpiece to be heated. For highheating eiiiciency it is necessary that the work coil and the workpiecebe closely coupled together, that is in closely spaced relationship toeach other, therefore, the size and shape of the apertures depend on thesize and shape of the workpiece to be heated.

In order to have a continuous path for the high frequency current, theplate is further provided with a slot or a out which extends from theperipheral surface of the plate and intersects the aperture or aperturesthereby forming a single conductor turn having first and second legmembers to allow the current to flow from the source through the legmember of the conductor on one side of the slot and return to the sourcethrough the leg member of the conductor on the other side of the slot.If the work coil is to have a number of turns the plates are assembledwith corresponding workpiece receiving apertures in axial alignmentforming a passage and the plates connected together electrically, eitherin series or in parallel.

When the work coil is energized the current flows through each plate buthas a tendency to concentrate more at the edges formed by the sides ofthe slot intersecting the wall of the aperture causing portions of theworkpiece nearest these edges to become overheated. The overheatedportion of the workpiece is commonly referred to as a hot spot. Workcoils constructed from the teaching of the prior art are assembled withthese edges aligned along a common axis which results in the workpiecehaving a number of hot spots substantially in a straight line. Thisalignment of hot spots adversely changes the metallurgicalcharacteristics of the workpiece because of the intense heatconcentration along a relatively narrow strip of the workpiece.

To overcome this disadvantage, it is proposed according to the presentinvention to offset in adjacent plates the corresponding edges formed bythe intersection of the slot with each aperture, thereby providing formore uniform heat distribution in the workpiece. In other words, whenthe plates are assembled with corresponding 2,754,397 Patented July 10,1956 workpiece receiving apertures in axial alignment these formededges, instead of lying along a common line are offset perime'tricallywith respect to each other. By olisetting these edges perimetrically inadjacent plates the areas previously subject to overheating are now morewidely spaced apart, thus allowing the heat to dissipate more evenly.Further, by offsetting these edges any adverse change in themetallurgical characteristics of that portion of the workpiece which isnearest the edge will not appreciably affect the overall mechanicalcharacteristics of the workpiece.

it is therefore an object of the present invention to provide animproved work coil for uniformly heating a workpiece by high frequencyinduction.

Another object of the present invention is to provide an improved workcoil in which points of unequal heating, caused by edges formed by theintersection of a slot and the apertures, are offset so that thesepoints of unequal heating are more widely spaced apart.

Objects and advantages other than those ment ned above will be apparentfrom the following description when read in connection with the drawingin which:

Fig. l is a plan view showing a work coil embodying the presentinvention;

Fig. 2 is a sectional view of the work coil shown in Fig. 1 taken alongthe line ll-ll;

Fig. 3 is an end view of the work coil shown in Fig. 1;

Fig. 4 is a plan view of a T-shaped work coil embodying the presentinvention;

Fig. 5 is a sectional view of the T-shaped work coil shown in 4 takenalong the line VV;

Fig. 6 is a sectional View of the T-shapecl plate shown in Fig. 5 takenalong the line VlVi;

Fig. 7 is a plan view of an L-shaped work coil embodying the presentinvention;

Fig. 8 is a sectional view of the L-shaped work coil shown in Fig. 7taken along the line lllh flli;

Fig. 9 is a sectional view of the L-shaped work coil shown in Fig. 8taken along the line IXIX;

Fig. 10 shows another modification of the work coil shown in Fig. 1;

Fig. ll is a view in elevation of the coil shown in Fig.

the plate to form a conductor turn having 5' s end leg members 24 and25, respectively, posed on opposite sides of slot 22 joined adjacent theend of slot 22. The unjoined e each leg member is adapted to beconnected to a suitable source of high frequency current. Slot 22intersects each aperture resulting in a plurality of edges being formed.As shown, edges 26 to 29 are formed by slot 2'2 intersec ing apertureSimilar edges are formed in a like manner by slot 22 intersectingapertures 19 and 21.

The work coil is formed by assembling the plates in parallel spacedrelationship with corresponding apertures in axial alignment, that is,the apertures 19 of the different plates have a common axis, therebyforming a passage for substantially surrounding the workpiece which isto be heat treated. However, in order to offset edges 26 to 29 inadjacent plates around the perimeter of the passage, plate 17 isinverted with respect to the position of plates 16 and 18, so that legmember 25 of plate 17 is sandwiched between leg members 24 of plates 16and 18, resulting in these edges 26 to 29 being spaced or offset aroundthe perimeter of the passage.

Any suitable known means may be used to connect the plates together. Asshown, the plates are connected electrically in series by means of aconduit 30 which is brazed to the peripheral surfaces of each plate andwhich serves to mechanically brace the plates and to cool them sinceconduit 30 may be connected to a source of cooling liquid.

While the work coil illustrated in Fig. 1 shows three plates eachprovided with a set of three cylindrically shaped apertures of likesize, if desired, the work coil could have any suitable number of platesand the plates could be provided with any suitable number of aperturesof difierent sizes and shapes.

The work coil illustrated in Fig. 4 shows another embodiment of thepresent invention. The work coil of Fig. 4 comprises two T-shaped plates31 and 32. Each plate is provided with a plurality of polygonalapertures and a T-shaped slot 33 which cooperates with the apertures toform a conductor turn having pairs of first and second leg portions 34and 35, respectively, disposed on opposed sides of slot 33 in a mannersimilar to that described in relation to the work coil of Fig. l. Legportions 35 are integrally joined intermediate the ends of the plate.

Slot 33 intersects each aperture to form a plurality of edges 36 to 39.In plate 31 the edges 36 to 39 lie on one side of the plane of symmetrywhich contains the axes of the apertures while in plate 32 these edgeslie on the other side of that reference plane. The plates are assembledwith corresponding apertures in axial alignment, thereby forming apassage to substantially surround the workpiece to be heated. The edges36 to 39 associated with corresponding apertures are therefore oflsetaround the perimeter of the passage.

Fig. 7 illustrates an L-shaped work coil embodying another modificationof the present invention. The work coil comprises a plurality ofelectrically conductive plates 51 to 54, alternate plates being similar.Each plate is provided with apertures 56 and 57 which are cylindricaland a slot 55 which extends from the peripheral surface of the plate andintersects each aperture, thereby forming a conductor turn having firstand second leg members disposed on opposite sides of the slot. As shown,slot 55 intersects each aperture only once, thereby forming two edges.The slots are disposed in adjacent plates so as to intersectcorresponding apertures substantially on opposite sides of the passageformed when corresponding apertures are in axial alignment. Slot 55intersects aperture 56 to form a pair of edges 58, 59 in plate 51, andin plate 52 intersects aperture 56 to form another pair of edges 60, 61which are offset 180 arounds the periphery of the passage from edges 58,59. The plates are connected together in series in a manner similar tothat shown in Fig. l, but if desired any suitable means for connectingthe plates together may be used.

Fig. shows another modification of the present invention applied to awork coil arranged to have a number of parallel paths. The work coilshown in Fig. 10 comprises a plurality of parallel plates 61 to 64 whichare similar to the plates of the work coil shown in Figs. 1 and 2.However, in the work coil shown in Fig. 10 the plates are not in spacedrelationship with each other but are superposed one on another. As inFig. 1 edges 65 to 68 formed by the intersection ofthe slot 69 with eachaperture 70 are offset around the perimeter of each passage formed bycorresponding apertures. Since adjacent plates are reversed with respectto each other the first leg member 71 of one plate is superposed on thesecond leg member 72 of an adjacent plate. Further, since the width ofeach leg member varies in a predetermined manner as determined by theposition of the slot 69, part of each leg member overlaps the slot inadjacent plates. In order that the first and second leg members of eachplate are not shorted together by the overlapping parts, the latter aremade of a smaller thickness than the nonoverlapping parts of the legmembers which provides a spaced relationship between them. The work coilas formed, then as a plurality of parallel current paths, each pathcomprising a single plate. The work coil may be energized and cooled inany suitable manner.

Although but a few embodiments of the present invention have beenillustrated and described it will be apparent to those skilled in theart that various modifications may be made therein without departingfrom the spirit of the invention or from the scope of the appendedclaims.

It is claimed and desired to secure by Letters Patent:

1. A work coil adapted to be energized with a high frequency current forheat treating a workpiece by induction, said work coil comprising aplurality of electrically conductive plates, each said plate having anaperture and a slot extending from the peripheral surface of said plateand intersecting said aperture to cause said plate to form a conductorturn having first and second leg members disposed on opposite sides ofsaid slot, each intersection of said slot with said aperture forming apair of edges on the wall 811118.66 of said aperture, said plates beingassembled with corresponding apertures in axial alignment defining apassage for substantially surrounding said workpiece to be heated andwith each said pair of formed edges in one plate offset around theperimeter of said passage with respect to another pair of similarlyformed edges in an adjacent plate, and means for electrically connectingsaid plates together.

2. A work coil adapted to be energized with a high frequency current forheat treating a plurality of workpieces, said work coil comprising aplurality of electrically conductive plates, each said plate having aplurality of apertures and a slot extending from the peripheral surfaceof said plate and intersecting said apertures to cause said plate toform a conductor turn having first and second leg members disposed onopposite sides of said slot and integrally joined adjacent the end ofsaid slot, each intersection of said slot with each said apertureforming a pair of edges on the wall surface of said aperture, saidplates being assembled in parallel spaced relationship withcorresponding apertures in axial alignment defining a passage forsubstantially surrounding said workpiece, adjacent plates being invertedwith respect to each other to cause each said pair of formed edges inone of said adjacent plates to be offset around the perimeter of saidpassage with respect to each said pair of formed edges in the other saidadjacent plate, and means for connecting said plates in series.

3. A work coil adapted to be energized with a high frequency current forheat treating a plurality of workpieces, said work coil comprising aplurality of electrically conductive T-shaped plates, each said platehaving a plurality of apertures and a T-shaped slot extending from theperipheral surface of said plate and intersecting said apertures tocause said plate to form a conductor turn having pairs of first andsecond leg portions disposed on opposite sides of said slot, said pairof second leg portions being integrally joined inter mediate the ends ofsaid plate, the intersection of said slot with each said apertureforming a plurality of edges, said plates being assembled in parallelspaced relation ship with corresponding apertures in axial alignmentforming a passage for substantially surrounding said workpiece, saidformed edges in said plates being offset around the perimeter of saidpassage, and means for connecting said plates in series.

4. A work coil adapted to be energized with a high frequency current tosimultaneously heat treat a plurality of workpieces by induction, saidwork coil comprising a plurality of electrically conductive L-shapedplates, each said plate having a plurality of apertures and a slotextending from the peripheral surface of said plate and intersectingsaid apertures to cause said plate to form a conductor turn having firstand second leg portions disposed on opposite sides of said slot andintegrally joined adjacent one of said apertures, the intersection ofsaid slot with each said aperture forming a plurality of edges, saidplates being assembled with corresponding apertures in axial alignmentforming a passage for substantially surrounding one of said plurality ofworkpieces to be heated, said formed edges associated with correspondingapertures in adjacent plates being otfset around the perimeter of saidpassage, and means for connecting said plates electrically in series.

5. A work coil adapted to be energized with a high frequency current tosimultaneously heat treat a plurality of workpieces by induction, saidwork coil comprising a plurality of electrically conductive plates, eachsaid plate having a plurality of apertures and a slot extending from theperipheral surface of said plate and intersecting said apertures tocause said plate to form a conductor turn having first and second legmembers disposed on opposite sides of said slot and integrally joinedadjacent the end of said slot, the intersection of said slot with eachsaid aperture forming a plurality of edges, said plates being assembledwith corresponding apertures in axial alignment forming passages forsubstantially surrounding said plurality of workpieces to be heated,adjacent plates being reversed With respect to each other to causesimilar portions of said leg members of said adjacent plates to overlap,said overlapping similar portions having a smaller thickness than thenonoverlapping portions to provide for a spaced relation between saidoverlapping portions, said formed edges associated with correspondingapertures in adjacent plates being ofiset around the perimeter of saidpassage.

References Cited in the file of this patent UNITED STATES PATENTS2,271,916 Denneen et a1. Feb. 3, 1942 2,394,944 Stanton Feb. 12, 19462,408,229 Roberds Sept. 24, 1946 2,481,071 Bowlus Sept. 6, 19492,643,325 Body et a1 June 23, 1953 2,689,296 Sabol Sept. 14, 1954FOREIGN PATENTS 684,495 Great Britain Dec. 17, 1952

